From 7716506adac4664793a9d6d3dfa31ffddfa98714 Mon Sep 17 00:00:00 2001 From: "Matthew Wilcox (Oracle)" Date: Tue, 4 May 2021 18:32:45 -0700 Subject: [PATCH] mm: introduce and use mapping_empty() Patch series "Remove nrexceptional tracking", v2. We actually use nrexceptional for very little these days. It's a minor pain to keep in sync with nrpages, but the pain becomes much bigger with the THP patches because we don't know how many indices a shadow entry occupies. It's easier to just remove it than keep it accurate. Also, we save 8 bytes per inode which is nothing to sneeze at; on my laptop, it would improve shmem_inode_cache from 22 to 23 objects per 16kB, and inode_cache from 26 to 27 objects. Combined, that saves a megabyte of memory from a combined usage of 25MB for both caches. Unfortunately, ext4 doesn't cross a magic boundary, so it doesn't save any memory for ext4. This patch (of 4): Instead of checking the two counters (nrpages and nrexceptional), we can just check whether i_pages is empty. Link: https://lkml.kernel.org/r/20201026151849.24232-1-willy@infradead.org Link: https://lkml.kernel.org/r/20201026151849.24232-2-willy@infradead.org Signed-off-by: Matthew Wilcox (Oracle) Tested-by: Vishal Verma Acked-by: Johannes Weiner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/block_dev.c | 2 +- fs/dax.c | 2 +- fs/gfs2/glock.c | 3 +-- include/linux/pagemap.h | 5 +++++ mm/truncate.c | 18 +++--------------- 5 files changed, 11 insertions(+), 19 deletions(-) diff --git a/fs/block_dev.c b/fs/block_dev.c index a5244e0..9114e0a 100644 --- a/fs/block_dev.c +++ b/fs/block_dev.c @@ -79,7 +79,7 @@ static void kill_bdev(struct block_device *bdev) { struct address_space *mapping = bdev->bd_inode->i_mapping; - if (mapping->nrpages == 0 && mapping->nrexceptional == 0) + if (mapping_empty(mapping)) return; invalidate_bh_lrus(); diff --git a/fs/dax.c b/fs/dax.c index b3d27fd..999f3f22 100644 --- a/fs/dax.c +++ b/fs/dax.c @@ -965,7 +965,7 @@ int dax_writeback_mapping_range(struct address_space *mapping, if (WARN_ON_ONCE(inode->i_blkbits != PAGE_SHIFT)) return -EIO; - if (!mapping->nrexceptional || wbc->sync_mode != WB_SYNC_ALL) + if (mapping_empty(mapping) || wbc->sync_mode != WB_SYNC_ALL) return 0; trace_dax_writeback_range(inode, xas.xa_index, end_index); diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c index 84c3810..ea7fc5c 100644 --- a/fs/gfs2/glock.c +++ b/fs/gfs2/glock.c @@ -273,8 +273,7 @@ static void __gfs2_glock_put(struct gfs2_glock *gl) if (mapping) { truncate_inode_pages_final(mapping); if (!gfs2_withdrawn(sdp)) - GLOCK_BUG_ON(gl, mapping->nrpages || - mapping->nrexceptional); + GLOCK_BUG_ON(gl, !mapping_empty(mapping)); } trace_gfs2_glock_put(gl); sdp->sd_lockstruct.ls_ops->lm_put_lock(gl); diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index 469fa7f..a4bd411 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -18,6 +18,11 @@ struct pagevec; +static inline bool mapping_empty(struct address_space *mapping) +{ + return xa_empty(&mapping->i_pages); +} + /* * Bits in mapping->flags. */ diff --git a/mm/truncate.c b/mm/truncate.c index 4559442..adb8d41 100644 --- a/mm/truncate.c +++ b/mm/truncate.c @@ -295,7 +295,7 @@ void truncate_inode_pages_range(struct address_space *mapping, pgoff_t index; int i; - if (mapping->nrpages == 0 && mapping->nrexceptional == 0) + if (mapping_empty(mapping)) goto out; /* Offsets within partial pages */ @@ -440,9 +440,6 @@ EXPORT_SYMBOL(truncate_inode_pages); */ void truncate_inode_pages_final(struct address_space *mapping) { - unsigned long nrexceptional; - unsigned long nrpages; - /* * Page reclaim can not participate in regular inode lifetime * management (can't call iput()) and thus can race with the @@ -452,16 +449,7 @@ void truncate_inode_pages_final(struct address_space *mapping) */ mapping_set_exiting(mapping); - /* - * When reclaim installs eviction entries, it increases - * nrexceptional first, then decreases nrpages. Make sure we see - * this in the right order or we might miss an entry. - */ - nrpages = mapping->nrpages; - smp_rmb(); - nrexceptional = mapping->nrexceptional; - - if (nrpages || nrexceptional) { + if (!mapping_empty(mapping)) { /* * As truncation uses a lockless tree lookup, cycle * the tree lock to make sure any ongoing tree @@ -633,7 +621,7 @@ int invalidate_inode_pages2_range(struct address_space *mapping, int ret2 = 0; int did_range_unmap = 0; - if (mapping->nrpages == 0 && mapping->nrexceptional == 0) + if (mapping_empty(mapping)) goto out; pagevec_init(&pvec); -- 2.7.4